Steam turbine system for a power plant

ABSTRACT

A steam turbine system for a power generating plant is provided. The steam turbine in the system has a live steam control valve at its live steam inlet, an extraction steam outlet, a live steam bypass line with a throttle valve which is connected to the inlet of the live steam control valve and also to the extraction steam outlet for directing live steam, which is throttled with the throttle valve, from upstream of the live steam control valve to the extraction steam outlet. The steam turbine with the live steam control valve and the live steam bypass line with the throttle valve are designed such that the steam turbine can be operated both in the nominal operating state with 100% live steam mass flow and in a special operating state with live steam mass flow above 100%, with a fully open live steam control valve in each case.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2009/053924, filed Apr. 2, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08007316.6 EP filed Apr. 14, 2008. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention refers to a steam turbine system for a power generating plant, and to the power generating plant with the steam turbine system.

BACKGROUND OF INVENTION

A nuclear power generating plant is operated for example with a pressurized water reactor. Fuel elements, in which heat which is created as a result of atomic disintegration reactions is released, are provided in the pressurized water reactor. The heat is dissipated by a cooling medium, for example water, with which live steam is produced in a steam generator. The live steam is guided in a live steam line to a steam turbine which is coupled to a generator for driving it. By the live steam in the steam turbine being expanded to condenser pressure, the steam turbine and the generator are driven for power generation. At the outlet of the steam turbine a condenser is provided, in which the expanded steam is condensed, using a cooling medium, and fed again to the steam generator.

Furthermore, the steam turbine has an extraction steam outlet by means of which extraction steam is tapped for further use in the nuclear power generating plant. The driving power of the steam turbine is determined by the temperature and the static pressure of the live steam, by the static pressure in the condenser, and also by the mass flow of the live steam which enters the steam turbine, and by the mass flow of the extraction steam which is tapped at a specific pressure level of the steam turbine.

For controlling the mass flow of the live steam (power output of the steam turbine) a live steam control valve is provided on the steam turbine. In the design of the steam turbine, a nominal operating state is defined, at which the temperature and the static pressure of the live steam and also the mass flow of the live steam is determined. In the nominal operating state (guarantee point of a steam turbine system), the live steam mass flow is defined at 100%. In the design of the steam turbine, however, an operating range is to be taken into consideration which is determined as a result of a variation of the temperature and of the static pressure of the live steam and also of the live steam mass flow. Therefore, the steam turbine is designed for example for a steady-state partial load operation with constant mean cooling medium temperature in the upper load range. During this partial load operation, a live steam pressure characteristic of the steam generator is established for the upper load range, which with increasing power output of the reactor has a falling static pressure of the live steam (so-called “negative sliding pressure”). In addition, operating conditions in the case of increased live steam mass flow compared with nominal load operation (for example 103% to 107% live steam mass flow) are to be taken into consideration. The steam turbine in this case is operated with fully open live steam valves. Such operating conditions require throttling of the live steam control valve in the nominal operating state with 100% live steam mass flow.

Another operating state which is to be taken into consideration in the design of the steam turbine is characterized by a reduced static pressure of the live steam. In this operating state, the live steam control valve is fully open with nominal, or less, live steam volume of the steam generator/reactor, so that the static pressure of the live steam is reduced and lowering of the cooling medium temperature takes place as a result (so-called “stretch-out mode”). The reduction of the static pressure of the live steam leads to an increase of the specific live steam volume, as a result of which heavy throttling of the live steam control valve in the nominal operating state is required.

A performance guarantee for the steam turbine is conventionally related to the nominal operating state which is operable only with the throttled live steam control valve. Operation of the steam turbine with the throttled live steam valve is inefficient, as a result of which the thermal efficiency of the nuclear power generating plant is lowered.

SUMMARY OF INVENTION

It is the object of the invention to create a steam turbine system for a power generating plant, and the power generating plant with the steam turbine system, wherein the power generating plant has a high thermal efficiency.

The steam turbine system according to the invention for the power generating plant has a steam turbine, which at its live steam inlet has a live steam control valve, and has an extraction steam outlet, and has a live steam bypass line with a throttle valve which is connected to the inlet of the live steam control valve and also to the extraction steam outlet for directing live steam, which is throttled by the throttle valve, from upstream of the live steam control valve to the extraction steam outlet, wherein the steam turbine with the live steam control valve and the live steam bypass line with the throttle valve are designed in such a way that the steam turbine can be operated both in the nominal operating state with 100% live steam mass flow and in a special operating state with over 100% live steam mass flow with a fully open live steam control valve in each case, wherein surplus live steam mass flow, compared with the nominal operating state, can be directed past the steam turbine at the inlet of the live steam control valve via the live steam bypass line, or, with 100% live steam mass flow, lowering of the static pressure of the live steam can be achieved by bypassing a predetermined portion of the live steam mass flow via the live steam bypass line.

As a result, the portion of live steam, which is delivered by a steam generator over and above the 100% live steam mass flow, is not fed directly to the steam turbine but via the live steam bypass line is guided past the live steam control valve and fed into the extraction steam outlet at extremely high static pressure. Therefore, during nominal operation of the steam turbine the live steam control valve is fully open, as a result of which a loss of efficiency due to a possible throttling of the live steam valve does not arise. The 100% live steam mass flow corresponds to the live steam mass flow during the nominal operating state of the steam turbine.

Furthermore, less or no extraction steam needs to be tapped from the steam turbine since the live steam in the live steam bypass line which is directed past the steam turbine is fed to the extraction steam outlet. Therefore, the thermal efficiency of the steam turbine system in a broad operating range of the steam turbine is high.

As a result of the steam turbine system having a broad operating range the power generating plant is in the position to participate in a frequency control/back-up of a network. If the power generating plant for example is a nuclear power generating plant, then with the steam turbine system possible power reserves of the nuclear reactor can be utilized without a conversion of the steam turbine in the corresponding operating mode, wherein the steam turbine system has a high thermal efficiency in the nominal operating state.

Furthermore, the nuclear power generating plant has a higher operational flexibility, as a result of which a fuel change in the nuclear power generating plant can be delayed so that a higher burn-up of the fuel rods can be achieved. In so doing, the nuclear power generating plant is to be operated in the so-called “stretch-out” mode during which the increased reactivity can be achieved by lowering the pressure of the live steam.

In particular, the steam turbine system according to the invention has high thermal efficiency if the steam turbine is a saturated steam engine with a low live steam state and therefore a reduced expansion gradient. With the steam turbine system according to the invention, in the nominal operating state the steam turbine, with 100% live steam mass flow, is operated with the live steam control valve fully open so that in a wide operating range of the steam turbine system throttling of the live steam control valve in the nominal operating state does not need to be provided. This is advantageous since with a one-percent throttling of the live steam control valve in the nominal operating state a power output reduction of the steam turbine, with the same reactor power output, of 0.13% would already be envisaged. As a result, the avoidance of throttling the live steam control valve in the nominal operating state leads to a power output gain of the power generating plant due to the higher efficiency of the steam turbine system.

Furthermore, the thermodynamic guaranteed values of the steam turbine system according to the invention in the case of the performance guarantee are improved because corresponding throttling of the live steam control valves can be dispensed with.

The live steam mass flow in the special operating state is preferably 102% to 115% of the live steam mass flow in the nominal operating state.

Therefore, the power generating plant, if the power generating plant is a nuclear power generating plant, can utilize possible power reserves of the reactor/steam generator permanently in the steady-state operation or alternatively for short-term power release in case of requirements with regard to frequency control/back-up.

The steam turbine system preferably has a live steam line with an emergency stop valve, which for feeding the live steam mass flow to the live steam control valve is connected to this control valve, wherein the live steam bypass line, between the live steam control valve and the emergency stop valve of the live steam line, is connected to this live steam line.

As a result, the live steam bypass line, downstream of the emergency stop valve of the live steam line, is branched off from this live steam line, as a result of which the live steam bypass line is also protected by the emergency stop valve of the live steam line.

Furthermore, the emergency stop valve in the live steam bypass line is preferably designed as a control valve with a safety function. As a result, only a single valve advantageously needs to be provided in the live steam bypass line.

Alternatively, it is preferred that the live steam bypass line is connected upstream of the emergency stop valve. Furthermore, it is preferred that the live steam control valve is a quick-action control valve with a safety function for double protection. With this, the pipeline integration is advantageously simple and for a valve test operation no provision needs to be made for corresponding modifications so that limitations which are attributable to them can be prevented.

Furthermore, it is preferred that an emergency stop valve is provided at the live steam inlet, and that the live steam bypass line has an emergency stop valve which is installed upstream of the throttle valve.

As a result, in addition to the emergency stop valve in the live steam line the steam turbine is additionally protected at its live steam inlet and the bypass line is protected.

It is preferred that the emergency stop valve of the live steam bypass line is connected to the emergency stop valve at the live steam inlet so that the emergency stop valve of the live steam bypass line operates with the emergency stop valve at the live steam inlet.

As a result, the emergency stop valves at the live steam inlet and of the live steam bypass line are operated synchronously, as a result of which the operation of the steam turbine is safer.

Moreover, it is preferred that the throttle valve is connected to the extraction steam inlet so that the throttle valve restricts the live steam to the extraction steam pressure in the extraction steam outlet.

As a result, the bypass mass flow via the live steam bypass line is controlled by the throttle valve so that in the live steam line, with the live steam control valves fully open, the live steam pressure which is required from the reactor/steam generator can be adjusted.

It is preferred that the steam turbine system has an extraction steam line which is connected to the extraction steam outlet and into which leads the live steam bypass line.

For superheating the live steam, the power generating plant according to the invention with the steam turbine system has a reheater to which the extraction steam can be fed.

The steam turbine system has the live steam bypass line by means of which live steam is fed to the extraction steam by the throttle valve. Consequently, for superheating the live steam, the live steam which is guided past the steam turbine via the live steam bypass line is fed to the reheater, as a result of which the power generating plant has a high thermal efficiency.

It is preferred that the reheater is constructed with two stages.

The bypass mass flow, which is generated as a result of the additional heating steam requirement of the first reheater stage, can be significantly increased before a direct introduction of the throttled bypass mass flow into the steam turbine occurs.

Furthermore, it is preferred that at the extraction steam outlet a check valve is provided, upstream of which the live steam bypass line enters.

As a result, a high pressure admitted from outside at the extraction steam outlet, leading to a backflow to the extraction steam outlet, is advantageously prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following text, preferred exemplary embodiments of the steam turbine system according to the invention are explained with reference to the attached schematic drawings. In the drawing:

FIGS. 1 and 2 show a schematic view of a first exemplary embodiment of the steam turbine system according to the invention and of the power generating plant according to the invention, and

FIG. 3 shows a schematic view of a first exemplary embodiment of the steam turbine system according to the invention.

DETAILED DESCRIPTION OF INVENTION

As is apparent from FIGS. 1 and 2, a steam turbine system 100 has a steam turbine 110 and a steam turbine 111. The steam turbines 110 and 111 have a live steam inlet 112 to 115 for the entry of live steam, and an extraction steam outlet 116 for the tapping of extraction steam. For controlling the live steam feed to the steam turbines 110 and 111, live steam control valves 117 to 120 are provided at the live steam inlets 112 to 115. For protecting the live steam inlets 112 to 115 and the steam turbine emergency stop valves 121 to 124 are connected to these.

Furthermore, the steam turbine system 100 has live steam lines 125 to 128 which are connected in each case to the live steam inlets 112 to 115. Moreover, an extraction steam line 129 is provided at the extraction steam outlet 116.

The steam turbine system 100 has a live steam bypass line 130 which is connected to the inlet of the live steam control valves 117 to 120 and to the extraction steam outlet 116 so that in the live steam bypass line 130 live steam from the inlet of the live steam control valves 117 to 120 to the extraction steam outlet 116 can be directed past the steam turbines 110 and 111. Alternatively, according to FIG. 3 the live steam bypass line 130 is connected upstream of the emergency stop valve.

In the live steam bypass line 130, as seen in the flow direction, an emergency stop valve 131 is first provided and a throttle valve 132 following it. The emergency stop valve 131 is connected to the emergency stop valve 121 so that the two stop valves 121 to 124, and 131, operate synchronously when correspondingly reaching an operating event (for example an overspeed). The throttle valve 132 is controlled in dependence upon the steam pressure downstream of the live steam bypass line 130 so that the live steam from the inlet of the live steam control valves 117 to 120 to the extraction steam outlet 116 is throttled.

Live steam lines 125 to 128, in which live steam is made available for operating the steam turbines 110 and 111, are provided at the outlet of the live steam control valves 117 to 120. Emergency stop valves 146 to 149 for protecting the live steam inlets and the steam turbine are provided in the live steam lines 125 to 128. In addition, check valves 170 and 171 are provided in the extraction line 129, with which a backflow in the extraction steam line 129 can be prevented.

The live steam bypass line 130 branches into the live steam lines 125 to 128 between the emergency stop valves 146 to 149 and the inlet of the live steam control valves 117 to 120 and leads into the extraction steam line 129 between the check valve 171 and the extraction steam outlet 116.

For controlling the pressure in the live steam lines 125 to 128, control valves 150 and 151 are provided parallel to the emergency stop valves 146 to 149.

In addition, the steam turbine system 100 has reheaters 140 and 141 which in each case have a first reheater stage 142 and 143 and also a second reheater stage 144 and 145. Second heating lines 162 and 163, in which extraction steam is fed to the first reheater stages 142 and 143, branch from the extraction steam line 129 downstream of the check valve 170. First heating steam lines 160 and 161 for feeding live steam which is fed into the live steam line 125 to 128 upstream of the emergency stop valves 146 to 149, are provided at the second reheater stages 144 and 145. 

1.-8. (canceled)
 9. A steam turbine system for a power generating plant, comprising: a steam turbine, comprising: a live steam inlet; a live steam control valve; an extraction steam outlet; an extraction steam line; a live steam bypass line; a live steam control valve; and a throttle valve, wherein the live steam inlet is connected to the live steam control valve, wherein the extraction steam outlet is connected to the extraction steam line, wherein the live steam bypass line is connected to the live steam control valve, and wherein the live steam bypass line leads into the extraction steam line.
 10. The steam turbine system as claimed in claim 9, wherein the steam turbine system includes a live steam line with a first emergency stop valve, wherein the first emergency stop valve is connected to the live steam control valve to feed a live steam mass flow to the live steam control valve, and wherein the live steam bypass line, between the live steam control valve and the first emergency stop valve of the live steam line, is connected to the live steam line, or is connected upstream of the first emergency stop valve.
 11. The steam turbine system as claimed in claim 10, wherein the first emergency stop valve is provided at the live steam inlet, and wherein the live steam bypass line includes a second emergency stop valve which is installed upstream of the throttle valve.
 12. The steam turbine system as claimed in claim 11, wherein the second emergency stop valve of the live steam bypass line is connected to a third emergency stop valve at the live steam inlet so that the second emergency stop valve of the live steam bypass line operates with the third emergency stop valve at the live steam inlet.
 13. The steam turbine system as claimed in claim 12, wherein the throttle valve is connected to the extraction steam outlet so that the throttle valve restricts live steam to an extraction steam pressure in the extraction steam outlet.
 14. A power generating plant, comprising: a steam turbine system, comprising: a steam turbine, comprising: a live steam inlet; a live steam control valve; an extraction steam outlet; an extraction steam line; a live steam bypass line; a live steam control valve; and a throttle valve, wherein the live steam inlet is connected to the live steam control valve, wherein the extraction steam outlet is connected to the extraction steam line, wherein the live steam bypass line is connected to the live steam control valve, and wherein the live steam bypass line leads into the extraction steam line; and a reheater, wherein the reheater superheats live steam to which the extraction steam can be fed.
 15. The power generating plant as claimed in claim 14, wherein the reheater is constructed with two stages.
 16. The power generating plant as claimed in 14, wherein at the extraction steam outlet a check valve is provided, upstream of which the live steam bypass line enters.
 17. The power generating plant as claimed in claim 14, wherein the power generating plant is a nuclear power generating plant. 